1. Field of the Invention
This invention relates to check-valved pouches and a manufacturing apparatus therefor. More particularly, the invention relates to check-valved pouches in each of which a check valve has a filter surface formed in a lower portion thereof in order to prevent a powdery or granular substance contained in the pouch from leaking out through a passage in the check valve or clogging the passage when gases are discharged from inside the pouch. The invention also relates to an apparatus for manufacturing such pouches. Further, the invention relates to check valves for use with the above pouches.
2. Description of the Related Art
Several types of check-valved pouches as noted above have been manufactured heretofore. For example, a check valve formed of plastic film is attached to a lateral edge of a main pouch body formed also of plastic film, for discharging gases from inside the main pouch body. A desired substance is placed in the the main pouch body, an interior of the main pouch body being communicable with the ambient only through a gas discharge passage in the check valve. The check valve includes a filter surface formed in a portion thereof inserted into the main pouch body, the filter surface being in communication with the gas discharge passage.
In the check-valved pouch having the above construction, the check valve has a valve body formed of thin plastic film, and the filter surface is defined by a thin plastic filtering film. The gas discharge passage is formed in a very narrow space between the plastic film and filter surface. Consequently, the filter surface tends to stick to an inner surface of the plastic film, thereby to close the gas discharge passage. This gives rise to a serious problem that the gases cannot be discharged from inside the pouch.